In seismic exploration, acoustic waves are generated and sent downward into the earth. Reflections occur at the interfaces of surface strata whose acoustic impedances differ and are subsequently detected by groups of geophones positioned at the earth's surface. Each geophone group (which can comprise a number of individual geophones) produces a composite electrical signal which drives indicating and recording equipment, usually located in a recording truck, the equipment being electrically connected to the geophone group through a geophone cable or segment of such a cable.
Whether the acquisition of the seismic data occurs in remote regions of the world or in more urban areas, the geophones of each geophone group should be frequently tested; only recently has the importance of such testing been documented; it has been found that perhaps up to 20% of the geophones used on a daily basis may be found defective in some way that is undetectable by the field crew using conventional techniques.
Prior art methods related to impulse testing of geophones in a field environment are somewhat limited. For example, it may be desirable to detect the first and second adjacent absolute peak voltages of the damped sinusoidal voltage as a function of the same common impulse response, i.e., commoncycle testing. From such amplitude data, the damping factor (b) and the relative sensitivity (G) of the geophones can be determined with greater accuracy. With regard to the latter, the prior art systems of which we are aware do not provide adjacent peak amplitude value on a common cycle or within the accuracies that have now been found desirable for proper evaluation of geophones.